1. Field of the Invention
This invention pertains to process parameter sensors and related operating methods and program products, and more particularly, to vibrating conduit process parameter sensors and related operating methods and computer program products.
2. Statement of the Problem
Coriolis effect mass flowmeters are commonly used to measure mass flow and other information for materials flowing through a conduit. Exemplary Coriolis flowmeters are disclosed in U.S. Pat. Nos. 4,109,524 of Aug. 29, 1978, 4,491,025 of Jan. 1, 1985, and Re. 31,450 of Feb. 11, 1982, all to J. E. Smith et al. These flowmeters typically include one or more conduits having a straight or a curved configuration. Each conduit may be viewed as having a set of vibration modes, including, for example, simple bending, torsional, radial and coupled modes. In a typical mass flow measurement application, each conduit is driven to oscillate at resonance in one of its natural modes as a material flows through the conduit. The vibration modes of the vibrating, material-filled system are affected by the combined mass and stiffness characteristics of the conduits and the characteristics of the material flowing within the conduits.
A typical component of a Coriolis flowmeter is the drive or excitation system. The drive system operates to apply a periodic physical force to the conduit that causes the conduit to oscillate. The drive system typically includes at least one actuator mounted to the conduit(s) of the flowmeter. The actuator typically contains one of many well known electromechanical devices, such as a voice coil device having a magnet mounted to a first conduit and a wire coil mounted to a second conduit, in an opposing relationship to the magnet. A drive circuit continuously applies a periodic, e.g., a sinusoidal or square wave, drive signal to the actuator coil. The periodic drive signal causes the actuator to drive the two conduits in an opposing periodic pattern that is thereafter maintained.
When there is effectively xe2x80x9czeroxe2x80x9d flow through a driven flowmeter conduit, points along the conduit tend to oscillate with approximately the same phase or a xe2x80x9czero-flowxe2x80x9d phase with respect to the driver, depending on the mode of the driven vibration. As material begins to flow from an inlet of the flowmeter, through the conduit and out of an outlet of the flowmeter, Coriolis forces arising from the material flow tend to induce phase shifts between spatially separate points along the conduit. Generally, as material flows through the conduit, the phase on the inlet side of the conduit lags the driver, while the phase on the outlet side of the conduit leads the driver. The phase shift induced between two locations on the conduit is approximately proportional to the mass flow rate of material through the conduit.
To measure mass flow rate, conventional Coriolis flowmeters typically measure phase at two transducers located near respective ends of the conduit, symmetrically placed with respect to a centrally positioned driver. However, manufacturing-induced asymmetries in transducer placement as well as other structural asymmetries and nonlinearities in the conduit structure may cause measurement inaccuracies. In addition, in some applications it may be desirable to utilize asymmetric transducer placements.
In light of the foregoing, it is an object of the present invention to provide process parameter sensors and related operating methods and computer program products that can provide more flexible and accurate techniques for measurement of process parameters such as mass flow rate, totalized mass flow and the like.
This and other objects, features and advantages are provided according to the present invention by vibrating conduit process parameter sensors and related operating methods and computer program products in which a process parameter associated with a material in a conduit of a sensor is estimated based on an estimated complex modal transformation. For example, an unknown mass flow may be estimated by estimating a complex modal transformation relating motion signals representing motion of the process parameter sensor conduit at the unknown mass flow to a complex eigenvector representing motion of the process parameter sensor conduit at the known mass flow. A plurality of complex measured values may be generated from the motion signals, and then used to estimate the complex modal transformation according to a best-fit technique such as a linear regression. According to an aspect of the present invention, motion signals representing motion at more than two locations are received, providing an overdetermined set of measurement data that can be used to produce a more accurate process parameter estimate. Complex modal transformation and process parameter estimation operations may be implemented in a microprocessor, digital signal processor (DSP) or similar computer.
By using a complex modal representation of the motion of a sensor conduit, the present invention can provide more flexible and accurate techniques for measuring process parameters such as mass flow in comparison to conventional measurement techniques. According to the present invention, a At variety of different types of measurements can provide the needed complex information. In addition, the estimation techniques utilized according to the present invention are well suited to using overdetermined sets of measurements.
In particular, according to the present invention, a process parameter is estimated by a parameter sensor having a conduit configured to contain material from a material processing system. A plurality of motion signals is received from a plurality of motion transducers. Each of the plurality of motion signals indicating indicates motion at one of a plurality of locations on the conduit. A complex modal transformation is estimated from the received plurality of motion signals, and a process parameter for the material processing system is estimated from the estimated complex modal transformation.
According to an aspect of the present invention, a complex eigenvector is provided representing the motion of the conduit at a plurality of locations at a known mass flow. A plurality of motion signals is received from the plurality of motion transducers, the plurality of motion signals indicating motion at a plurality of locations on the conduit as a material flows through the conduit. A complex modal transformation relating the received plurality of motion signals to the complex eigenvector is estimated. Mass flow through the conduit is estimated from the known mass flow and the estimated complex modal transformation.
According to another aspect of the present invention, a plurality of complex measured values is generated from the received plurality of motion signals, a respective one of the plurality of complex measured values corresponding to a respective one of the plurality of locations. A complex modal transformation relating the generated plurality of complex measured values to the complex eigenvector is estimated. According to another aspect of the present invention, a complex modal transformation is estimated by constructing a complex vector from the generated plurality of complex measured values, and by determining a scaled rotation relating the complex vector to the complex eigenvector.
According to yet another aspect of the present invention, a transformation which best fits the plurality of complex measured values to the complex eigenvector is determined, and mass flow is estimated from the known mass flow according to the determined transformation. Determination of a best fit transformation may include performing a linear regression to determine a transformation which best fits the plurality of complex measured values to the complex eigenvector.
According to spatial integration aspects of the present invention, a plurality of motion signals is received representing motion at more than two physically separate locations. A complex modal transformation is then estimated, relating the plurality of motion signals representing motion at the more than two physically separate locations to the complex eigenvector.
According to calibration aspects of the present invention, a plurality of motion signals are received from the plurality of motion transducers, the plurality of motion signals indicating motion at the plurality of locations at a known mass flow. A complex eigenvector is determined from the received plurality of motion signals, and a representation of the complex eigenvector is stored in the process parameter sensor.
A process parameter sensor according to the present invention includes a conduit configured to contain material from a material processing system. A plurality of motion transducers is operative to produce a plurality of motion signals indicating motion at a plurality of locations on the conduit. A complex modal transformation estimator is responsive to the plurality of motion transducers, configured to receive a plurality of motion signals from the plurality of motion transducers and operative to estimate a complex modal transformation from the received plurality of motion signals. A process parameter estimator is responsive to the complex modal transformation estimator and operative to estimate a process parameter for the material processing system from the estimated complex modal transformation. In an embodiment of the present invention, the complex modal transformation estimator comprises means for estimating a complex modal transformation relating the received plurality of motion signals to a complex eigenvector representing motion of the conduit at a known mass flow. The process parameter estimator comprises means for estimating mass flow through the conduit from the known mass flow and the estimated complex modal transformation.
According to another aspect of the present invention, a computer program product for determining a process parameter associated with a material in a conduit of a parameter sensor includes first computer readable program code means for receiving a plurality of motion signals representing motion at a plurality of locations on the conduit. Second computer readable program code means are responsive to the first computer readable program code means and estimate a complex modal transformation from the received plurality of motion signals. Third computer readable program code means are responsive to the second computer readable program code means and estimate a process parameter associated with a material in the conduit from the estimated complex modal transformation. Improved process parameter measurements may thereby be provided.